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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


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    ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture

    Bob Latino
    Bob Latino
    Bob Latino
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    Location : Massachusetts
    • Post n°1

    ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture Empty ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture

    Post by Bob Latino Fri Apr 10, 2009 8:15 pm

    I recently had a customer ask me about the date of manufacture of his ST-70. There is a code on the bias pots that gives you a good idea of what year your amp kit was shipped out by Dynaco. This also works for the Mark II, Mark III and Mark IV amps. Below is the text of the Email that I wrote in response to his Email.

    "Steve,

    On the ST-70 you can check the 7-digit number stamped on the bottom of the BIAS POTENTIOMETERS. The 4th and 5th digits are the year of manufacture and the 6th and 7th numbers are what week of that year. If for example the bias pot is numbered 1386217 - then these bias pots were made in the 17th week of 1962 - probably in early May of 1962. Since Dynaco used parts very quickly you can almost be assured that this amp kit was shipped to a dealer in 1962. If your bias pot has a "48 to 52" as the 6th and 7th numbers like "1386249" then it is possible that the pot was made in 1962 but the amp was shipped out 5 or 6 weeks later in 1963.

    See below a bias pot made in August of 1964 with a "1376430" code


    Bob"

    ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture Biaspotcode
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    • Post n°2

    ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture Empty Re: ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture

    Post by Guest Sat Apr 11, 2009 2:56 pm

    Good info Bob, thanks. The transformers often carry a date code, as well. The Mark II I am working on has a "57" stamped on the bottom of both transformers, and the numbers for the year on the bias pot are also "57." Kind of cool to be working on something from so long ago.

    Peter
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    Clik2media
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    Join date : 2009-01-18
    • Post n°3

    ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture Empty Re: ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture

    Post by Clik2media Mon Apr 13, 2009 7:35 pm

    Great info Bob, I was always curious about my stable of Dynaco's
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    Listens2tubes
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    Join date : 2009-04-08
    Location : New Jersey
    • Post n°4

    ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture Empty Re: ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture

    Post by Listens2tubes Thu Apr 16, 2009 8:22 pm

    What do you make of this. Both my MkIVs have the same bias pots. The amps are serial number 8014002 and 8047086 if that helps.
    ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture Mkivbi11
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    Bob Latino
    Bob Latino
    Bob Latino
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    Posts : 3276
    Join date : 2008-11-26
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    • Post n°5

    ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture Empty Re: ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture

    Post by Bob Latino Thu Apr 16, 2009 8:58 pm

    Since the "137" number starts both bias pots the "137" could refer to the part # from the manufacturer of these pots or possibly the machine they were made on ?

    My best guess is that the "9" refers to 1969 and the "52" refers to the 52nd (last week) of 1969. These amps were not made until 1960 so the "9" can't refer to 1959 and the Mark IV was out of production by 1979.

    I found another bias pot from another ST-70 in my pile of old Dynaco parts that has a 6 digit code like on your pot but this pot is stamped on the SIDE of the pot. This one reads "137808" - maybe made in the 8th week of 1968 ? If anyone has more definitive knowlege of the codes on the Dynaco bias pots let us know ?

    Bob

    ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture Biaspot2
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    Rowbo1
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    Join date : 2011-01-27
    • Post n°6

    ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture Empty Re: ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture

    Post by Rowbo1 Fri Jan 28, 2011 3:41 am

    To cool, 64
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    • Post n°7

    ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture Empty Re: ST-70, Mark II, Mark III and Mark IV - to check your date of manufacture

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